This invention relates to memory devices. In particular this invention provides a nonvolatile electronic memory device capable of storing information in extremely high density.
Basic functions of a computer include information processing and storage. In typical computer systems, these arithmetic, logic, and memory operations are performed by devices that are capable of reversibly switching between two states often referred to as xe2x80x9c0xe2x80x9d and xe2x80x9c1.xe2x80x9d In most cases, such switching devices are fabricated from semiconducting devices that perform these various functions and are capable of switching between two states at a very high speed using minimum amounts of electrical energy. Thus, for example, transistors and transistor variants perform the basic switching and storage functions in computers.
Because of the huge data storage requirements of modern computers, a new, compact, low-cost, very high capacity, high speed memory configuration is needed. To reach this objective, molecular electronic switches, wires, microsensors for chemical analysis, and opto-electronic components for use in optical computing have been pursued. The principal advantages of using molecules in these applications are high component density (upwards of 1018 bits per square centimeter), increased response speeds, and high energy efficiency.
A variety of approaches have been proposed for molecular-based memory devices. While these approaches generally employ molecular architectures that can be switched between two different states, all of the approaches described to date have intrinsic limitations making their uses in computational devices difficult or impractical.
For example, such approaches to the production of molecular memories have involved photochromic dyes, electrochromic dyes, redox dyes, and molecular machines. Each of these approaches, however, has intrinsic limitations that ultimately render it unsuitable for use in molecular memories. For example, photochromic dyes change conformation in response to the absorption of light (e.g. cis-trans interconversion of an alkene, ring opening of a spiropyran, interconversion between excited-states in bacteriorhodopsin, etc.). Typically, the molecular structure of the dye is interconverted abetween two states that have distinct spectral properties.
Reading and writing data with such photochromic dyes requires use of light, often in the visible region (400-700 nm). Light-mediated data storage has intrinsic diffraction-limited size constraints. Moreover, most photochromic schemes are limited to scanning and interrogating dyes deposited on a surface and are not amenable to 3-D data storage. Even with near-field optical approaches, which might allow reliable encoding/reading of data elements of 100xc3x97100 nm dimensions (Nieto-Vesperinas and Garcia, N., eds. (1996) Optics at the Nanometer Scale, NATO ASI Series E, Vol. 319, Kluwer Academic Publishers: Dordrecht) the inherent restricted dimensionality (2-D) limits data density to 1010 bits/cm2. Strategies for 3-dimensional reading and writing of photochromic systems have been proposed that rely on two-photon excitation of dyes to encode data, and one-photon excitation to read the data (Birge et al. (1994) Amer. Sci. 82: 349-355, Parthenopoulos and Rentzepis (1989) Science, 245: 843-845), but it is believed that no high-density memory cubes have reached prototype stage in spite of the passage of at least a decade since their initial proposition. In addition, it is noted that these dyes often exhibit relatively slow switching times ranging from microsecond to millisecond durations.
Electrochromic dyes have been developed that undergo a slight change in absorption spectrum upon application of an applied electric field (Liptay (1969) Angew. Chem., Int. Ed. Engl. 8: 177-188). The dyes must be oriented in a fixed direction with respect to the applied field. Quite high fields ( greater than 107 V/cm) must be applied to observe an altered absorption spectrum which can result in heat/power dissipation problems. In addition, the change in the absorption spectrum is typically quite small, which can present detection difficulties. The dyes revert to the initial state when the applied field is turned off.
Redox dyes have been developed that undergo a change in absorption spectrum upon chemical or electrochemical reduction (typically a 2-electron, 2-proton reduction) (Otsuki et al. (1996) Chem. Lett. 847-848). Such systems afford bistable states (e.g., quinone/hydroquinone, azo/hydrazo). Redox dyes have only been examined in solution studies, where they have been proposed for applications as switches and sensors (de Silva et al. (1997) Chem. Rev. 97: 1515-1566). On a solid substrate, electrochemical reduction would need to be accompanied by a source of protons. The latter requirement may be difficult to achieve on a solid substrate. Furthermore, any optical reading scheme would pose the same 2-D limitations as described for photochromic dyes.
Yet another approach involves the design of molecular machines (Anell et al. (1992) J. Am. Chem. Soc. 114: 193-218). These elegant molecular architectures have moving parts that can be switched from one position to another by chemical or photochemical means. The chemically induced systems have applications as sensors but are not practical for memory storage, while the photochemically induced systems have the same fundamental limitations as photochromic dyes. Moreover, methods have not yet been developed for delineating the conformation/structure of the molecular machine that are practical in any device applications. 1H NMR spectroscopy, for example, is clearly the method of choice for elucidating structure/conformation for molecules in solution, but is totally impractical for interrogating a molecular memory element. None of the current architectures for molecular machines has been designed for assembly on a solid substrate, an essential requirement in a viable device.
In summary, photochromic dyes, electrochromic dyes, redox-sensitive dyes, and molecular machines all have fundamental limitations that have precluded their application as viable memory elements. These molecular architectures are typically limited by reading/writing constraints. Furthermore, even in cases where the effective molecular bistability is obtained, the requirement for photochemical reading restricts the device architecture to a 2-dimensional thin film. The achievable memory density of such a film is unlikely to exceed 1010 bits/cm2. Such limitations greatly diminish the appeal of these devices as viable molecular memory elements.
This invention provides novel high density memory devices that are electrically addressable permitting effective reading and writing, that provide a high memory density (e.g., 1015 bits/cm3), that provide a high degree of fault tolerance, and that are amenable to efficient chemical synthesis and chip fabrication. The devices are intrinsically latchable, defect tolerant, and support destructive or non-destructive read cycles.
In a preferred embodiment, this invention provides an apparatus for storing data (e.g., a xe2x80x9cstorage cellxe2x80x9d). The storage cell includes a fixed electrode electrically coupled to a xe2x80x9cstorage mediumxe2x80x9d having a multiplicity of different and distinguishable oxidation states where data is stored in the (preferably non-neutral) oxidation states by the addition or withdrawal of one or more electrons from said storage medium via the electrically coupled electrode. In preferred storage cells, the storage medium stores data at a density of at least one bit, preferably at a density of at least 2 bits, more preferably at a density of at least 3 bits, and most preferably at a density of at least 5, 8, 16, 32, or 64 bits per molecule. Thus, preferred storage media have at least 2, 8, 16, 32, 64, 128 or 256 different and distinguishable oxidation states. In particularly preferred embodiments, the bits are all stored in non-neutral oxidation states. In a most preferred embodiment, the different and distinguishable oxidation states of the storage medium can be set by a voltage difference no greater than about 5 volts, more preferably no greater than about 2 volts, and most preferably no greater than about 1 volt.
The storage medium is electrically coupled to the electrode(s) by any of a number of convenient methods including, but not limited to, covalent linkage (direct or through a linker), ionic linkage, non-ionic xe2x80x9cbondingxe2x80x9d, simple juxtaposition/apposition of the storage medium to the electrode(s), or simple proximity to the electrode(s) such that electron tunneling between the medium and the electrode(s) can occur. The storage medium can contain or be juxtaposed to or layered with one or more dielectric material(s). Preferred dielectric materials are imbedded with counterions (e.g. Nafion). The storage cells of this invention are fully amenable to encapsulation (or other packaging) and can be provided in a number of forms including, but not limited to, an integrated circuit or as a component of an integrated circuit, a non-encapsulated xe2x80x9cchipxe2x80x9d, etc. In some embodiments, the storage medium is electronically coupled to a second electrode that is a reference electrode. In certain preferred embodiments, the storage medium is present in a single plane in the device. The apparatus of this invention can include the storage medium present at a multiplicity of storage locations, and in certain configurations, each storage location and associated electrode(s) forms a separate storage cell. The storage present on a single plane in the device or on multiple planes and said storage locations are present on multiple planes of said device. Virtually any number (e.g., 16, 32, 64, 128, 512, 1024, 4096, etc.) of storage locations and/or storage cells can be provided in the device. Each storage location can be addressed by a single electrode or by two or more electrodes. In other embodiments, a single electrode can address multiple storage locations and/or multiple storage cells.
In preferred embodiments, one or more of the electrode(s) is connected to a voltage source (e.g. output of an integrated circuit, power supply, potentiostat, microprocessor (CPU), etc.) that can provide a voltage/signal for writing, reading, or refreshing the storage cell(s). One or more of the electrode(s) is preferably connected to a device (e.g., a voltammetric device, an amperometric device, a potentiometric device, etc.) to read the oxidation state of said storage medium. In particularly preferred embodiments, the device is an impedance spectrometer or a sinusoidal voltammeter. Various signal processing methods can be provided to facilitate readout in the time domain or in the frequency domain. Thus, in some embodiments, the readout device(s) provide a Fourier transform (or other frequency analysis) of the output signal from said electrode. In certain preferred embodiments, the device refreshes the oxidation state of said storage medium after reading said oxidation state.
A wide variety of molecules can be used as storage molecules and hence comprise the storage medium. Preferred molecules include, but are not limited to a porphyrinic macrocycle, a metallocene, a linear polyene, a cyclic polyene, a heteroatom-substituted linear polyene, a heteroatom-substituted cyclic polyene, a tetrathiafulvalene, a tetraselenafalvalene, a metal coordination complex, a buckyball, a triarylamine, a 1,4-phenylenediamine, a xanthene, a flavin, a phenazine, a phenothiazine, an acridine, a quinoline, a 2,2xe2x80x2-bipyridyl, a 4,4xe2x80x2-bipyridyl, a tetrathiotetracene, and a peri-bridged naphthalene dichalcogenide. Even more preferred molecules include a porphyrin, an expanded porphyrin, a contracted porphyrin, a ferrocene, a linear porphyrin polymer, and a porphyrin array. Certain particularly preferred storage molecules include a porphyrinic macrocycle substituted at a xcex2-position or at a meso-position. Molecules well suited for use as storage molecules include the molecules described herein (e.g. the molecules of Formulas I-XXVIII).
Particularly preferred methods and/or devices of this invention utilize a xe2x80x9cfixedxe2x80x9d electrode. Thus, in one embodiment, methods and/or devices in which the electrode(s) are moveable (e.g. one or ore electrodes is a xe2x80x9crecording headxe2x80x9d, the tip of a scanning tunneling microscope (STM), the tip of an atomic force microscope (AFM), or other forms in which the electrode is movable with respect to the storage medium are excluded. In certain embodiments, methods and/or devices and/or storage media, and/or storage molecules in which the storage molecule is an alkanethiolferrocene are excluded. Similarly in certain embodiments, methods and/or devices and/or storage media, in which the storage molecules are responsive to light and/or in which the oxidation state of a storage molecule is set by exposure to light are excluded.
In another embodiment, this invention provides an information storage medium. The information storage medium can be used to assemble storage cells and/or the various memory devices described herein. In a preferred embodiment the storage medium comprises one or more different storage molecules. When different species of storage molecule are present, each species of storage molecule oxidation state(s) different from and distinguishable from the oxidation state(s) of the other species of storage molecule comprising the storage medium. In preferred embodiments, the storage molecule(s) include a porphyrinic macrocycle, a metallocene, a linear polyene, a cyclic polyene, a heteroatom-substituted linear polyene, a heteroatom-substituted cyclic polyene, a tetrathiafulvalene, a tetraselenafulvalene, a metal coordination complex, a buckyball, a triarylamine, a 1,4-phenylenediamine, a xanthene, a flavin, a phenazine, a phenothiazine, an acridine, a quinoline, a 2,2xe2x80x2-bipyridyl, a 4,4xe2x80x2-bipyridyl, a tetrathiotetracene, or a peri-bridged naphthalene dichalcogenide. In even more preferred embodiment, the storage molecule(s) include a porphyrin, an expanded porphyrin, a contracted porphyrin, a ferrocene, a linear porphyrin polymer, or a porphyrin array. Preferred storage molecules contain two or more covalently linked redox-active subunits. In various preferred embodiments, the storage molecules include any of the storage molecules as described herein (e.g. the molecules of Formulas I-XXVIII).
In still another embodiment this invention provides a collection of molecules for the production of a data storage medium. A preferred collection comprises a plurality of storage molecules wherein each species of storage molecule has an oxidation state different from and distinguishable from the oxidation states of the other species of storage molecules comprising the collection. In various preferred embodiments, the storage molecules include any of the storage molecules as described herein (e.g. the molecules of Formulas I-XXVIII).
This invention also provides particularly preferred molecules for the storage of information (storage molecules). The molecules preferably have at least one non-neutral oxidation state and more preferably have at least two different and distinguishable non-neutral oxidation states. In various preferred embodiments, the storage molecules include any of the storage molecules as described herein (e.g. the molecules of Formulas I-XXVIII).
This invention also provides methods of storing data. The methods involve i) providing an apparatus, e.g., comprising one or more storage cells as described herein; and ii) applying a voltage to the electrode at sufficient current to set an oxidation state of said storage medium (the storage medium comprising one or more storage cells). In preferred embodiments, the voltage ranges is less than about 5 volts, more preferably less than about 2 volts, and most preferably less than about 1 or less than about 0.5 volts. The voltage can be the output of any convenient voltage source (e.g. output of an integrated circuit, power supply, logic gate, potentiostat, microprocessor (CPU), etc.) that can provide a voltage/signal for writing, reading, or refreshing the storage cell(s).
The method can further involve detecting the oxidation state of the storage medium and thereby reading out the data stored therein. The detection (read) can optionally involve refreshing the oxidation state of the storage medium (particularly in static-hole devices). The read (detecting) can involve analyzing a readout signal in the time or frequency domain and can thus involve performing a Fourier transform on the readout signal. The detection can be by any of a variety of methods including, but not limited to a voltammetric method. One particularly preferred readout utilizes impedance spectroscopy. The readout (detecting) can involve exposing the storage medium to an electric field to produce an electric field oscillation having characteristic frequency and detecting the characteristic frequency. In preferred embodiments, the storage cells used in the methods of this invention have storage media comprising one or more of the storage molecules described herein (e.g. the molecules of Formulas I-XXVIII).
This invention additionally provides the memory devices of this invention (e.g. memory cells) in a computer system. In addition computer systems utilizing the memory devices of this invention are provided. Preferred computer systems include a central processing unit, a display, a selector device, and a memory device the storage devices (e.g. storage cells) of this invention.
The term xe2x80x9coxidationxe2x80x9d refers to the loss of one or more electrons in an element, compound, or chemical substituent/subunit. In an oxidation reaction, electrons are lost by atoms of the element(s) involved in the reaction. The charge on these atoms must then become more positive. The electrons are lost from the species undergoing oxidation and so electrons appear as products in an oxidation reaction. An oxidation is taking place in the reaction Fe2+(aq) xe2x88x92xe2x88x92 greater than Fe3+(aq)+exe2x88x92 because electrons are lost from the species being oxidized, Fe2+(aq), despite the apparent production of electrons as xe2x80x9cfreexe2x80x9d entities in oxidation reactions. Conversely the term reduction refers to the gain of one or more electrons by an element, compound, or chemical substituent/subunit.
An xe2x80x9coxidation statexe2x80x9d refers to the electrically neutral state or to the state produced by the gain or loss of electrons to an element, compound, or chemical substituent/subunit. In a preferred embodiment, the term xe2x80x9coxidation statexe2x80x9d refers to states including the neutral state and any state other than a neutral state caused by the gain or loss of electrons (reduction or oxidation).
The term xe2x80x9cmultiple oxidation statesxe2x80x9d means more than one oxidation state. In preferred embodiments, the oxidation states may reflect the gain of electrons (reduction) or the loss of electrons (oxidation).
The terms xe2x80x9cdifferent and distinguishablexe2x80x9d when referring to two or more oxidation states means that the net charge on the entity (atom, molecule, aggregate, subunit, etc.) can exist in two different states. The states are said to be xe2x80x9cdistinguishablexe2x80x9d when the difference between the states is greater than thermal energy at room temperature (e.g. 0xc2x0 C. to about 40xc2x0 C.).
The term xe2x80x9celectrodexe2x80x9d refers to any medium capable of transporting charge (e.g. electrons) to and/or from a storage molecule. Preferred electrodes are metals or conductive organic molecules. The electrodes can be manufactured to virtually any 2-dimensional or 3-dimensional shape (e.g. discrete lines, pads, planes, spheres, cylinders, etc.).
The term xe2x80x9cfixed electrodexe2x80x9d is intended to reflect the fact that the electrode is essentially stable and unmovable with respect to the storage medium. That is, the electrode and storage medium are arranged in an essentially fixed geometric relationship with each other. It is of course recognized that the relationship alters somewhat due to expansion and contraction of the medium with thermal changes or due to changes in conformation of the molecules comprising the electrode and/or the storage medium. Nevertheless, the overall spatial arrangement remains essentially invariant. In a preferred embodiment this term is intended to exclude systems in which the electrode is a movable xe2x80x9cprobexe2x80x9d (e.g. a writing or recording xe2x80x9cheadxe2x80x9d, an atomic force microscope (AFM) tip, a scanning tunneling microscope (STM) tip, etc.).
The term xe2x80x9cworking electrodexe2x80x9d is used to refer to one or more electrodes that are used to set or read the state of a storage medium and/or storage molecule.
The term xe2x80x9creference electrodexe2x80x9d is used to refer to one or more electrodes that provide a reference (e.g. a particular reference voltage) for measurements recorded from the working electrode. In preferred embodiments, the reference electrodes in a memory device of this invention are at the same potential although in some embodiments this need not be the case.
The term xe2x80x9celectrically coupledxe2x80x9d when used with reference to a storage molecule and/or storage medium and electrode refers to an association between that storage medium or molecule and the electrode such that electrons move from the storage medium/molecule to the electrode or from the electrode to the storage medium/molecule and thereby alter the oxidation state of the storage medium/molecule. Electrical coupling can include direct covalent linkage between the storage medium/molecule and the electrode, indirect covalent coupling (e.g. via a linker), direct or indirect ionic bonding between the storage medium/molecule and the electrode, or other bonding (e.g. hydrophobic bonding). In addition, no actual bonding may be required and the storage medium/molecule may simply be contacted with the electrode surface. There also need not necessarily be any contact between the electrode and the storage medium/molecule where the electrode is sufficiently close to the storage medium/molecule to permit electron tunneling between the medium/molecule and the electrode.
The term xe2x80x9credox-active unitxe2x80x9d or xe2x80x9credox-active subunitxe2x80x9d refers to a molecule or component of a molecule that is capable of being oxidized or reduced by the application of a suitable voltage.
The term xe2x80x9csubunitxe2x80x9d, as used herein, refers to a redox-active component of a molecule.
The terms xe2x80x9cstorage moleculexe2x80x9d or xe2x80x9cmemory moleculexe2x80x9d refer to a molecule having one or more oxidation states that can be used for the storage of information (e.g. a molecule comprising one or more redox-active subunits). Preferred storage molecules have two or more different and distinguishable non-neutral oxidation states.
The term xe2x80x9cstorage mediumxe2x80x9d refers to a composition comprising two or more storage molecules. The storage medium can contain only one species of storage molecule or it can contain two or more different species of storage molecule.
The term xe2x80x9cstorage mediumxe2x80x9d as used herein refers to a collection of storage molecules. Preferred storage media comprise a multiplicity (at least 2) of different and distinguishable (preferably non-neutral) oxidation states. The multiplicity of different and distinguishable oxidation states can be produced by the combination of different species of storage molecules, each species contributing to said multiplicity of different oxidation states and each species having a single non-neutral oxidation state. Alternatively or in addition, the storage medium can comprise one or more species of storage molecule having a multiplicity of non-neutral oxidation states. The storage medium can contain predominantly one species of storage molecule or it can contain a number of different storage molecules. The storage media can also include molecules other than storage molecules (e.g. to provide chemical stability, suitable mechanical properties, to prevent charge leakage, etc.).
The term xe2x80x9celectrochemical cellxe2x80x9d consists minimally of a reference electrode, a working electrode, a redox-active medium (e.g. a storage medium), and, if necessary, some means (e.g., a dielectric) for providing electrical conductivity between the electrodes and/or between the electrodes and the medium. In some embodiments, the dielectric is a component of the storage medium.
The terms xe2x80x9cmemory elementxe2x80x9d, xe2x80x9cmemory cellxe2x80x9d, or xe2x80x9cstorage cellxe2x80x9d refer to an electrochemical cell that can be used for the storage of information. Preferred xe2x80x9cstorage cellsxe2x80x9d are discrete regions of storage medium addressed by at least one and preferably by two electrodes (e.g. a working electrode and a reference electrode). The storage cells can be individually addressed (e.g. a unique electrode is associated with each memory element) or, particularly where the oxidation states of different memory elements are distinguishable, multiple memory elements can be addressed by a single electrode. The memory element can optionally include a dielectric (e.g. a dielectric impregnated with counterions).
The term xe2x80x9cstorage locationxe2x80x9d refers to a discrete domain or area in which a storage medium is disposed. When addressed with one or more electrodes, the storage location may form a storage cell. However if two storage locations contain the same storage media so that they have essentially the same oxidation states, and both storage locations are commonly addressed, they may form one functional storage cell.
Addressing a particular element refers to associating (e.g., electrically coupling) that memory element with an electrode such that the electrode can be used to specifically determine the oxidation state(s) of that memory element.
The term xe2x80x9cstorage densityxe2x80x9d refers to the number of bits per volume and/or bits per molecule that can be stored. When the storage medium is said to have a storage density greater than one bit per molecule, this refers to the fact that a storage medium preferably comprises molecules wherein a single molecule is capable of storing at least one bit of information.
The terms xe2x80x9creadxe2x80x9d or xe2x80x9cinterrogatexe2x80x9d refer to the determination of the oxidation state(s) of one or more molecules (e.g. molecules comprising a storage medium).
The term xe2x80x9crefreshxe2x80x9d when used in reference to a storage molecule or to a storage medium refers to the application of a voltage to the storage molecule or storage medium to re-set the oxidation state of that storage molecule or storage medium to a predetermined state (e.g. an oxidation state the storage molecule or storage medium was in immediately prior to a read).
The term xe2x80x9cExc2xdxe2x80x9d refers to the practical definition of the formal potential (Exc2x0) of a redox process as defined by E=Exc2x0+(RT/nF)ln(Dox/Dred) where R is the gas constant, T is temperature in K (Kelvin), n is the number of electrons involved in the process, F is the Faraday constant (96,485 Coulomb/mole), Dox is the diffusion coefficient of the oxidized species and Dred is the diffusion coefficient of the reduced species.
A voltage source is any source (e.g. molecule, device, circuit, etc.) capable of applying a voltage to a target (e.g. an electrode).
The term xe2x80x9cpresent on a single planexe2x80x9d, when used in reference to a memory device of this invention refers to the fact that the component(s) (e.g. storage medium, electrode(s), etc.) in question are present on the same physical plane in the device (e.g. are present on a single lamina). Components that are on the same plane can typically be fabricated at the same time, e.g., in a single operation. Thus, for example, all of the electrodes on a single plane can typically be applied in a single (e.g., sputtering) step (assuming they are all of the same material).
The phrase xe2x80x9coutput of an integrated circuitxe2x80x9d refers to a voltage or signal produced by a one or more integrated circuit(s) and/or one or more components of an integrated circuit.
A xe2x80x9cvoltammetric devicexe2x80x9d is a device capable of measuring the current produced in an electrochemical cell as a result of the application of a voltage or change in voltage.
An xe2x80x9camperometric devicexe2x80x9d is a device capable of measuring the current produced in an electrochemical cell as a result of the application of a specific potential field potential (xe2x80x9cvoltagexe2x80x9d).
A potentiometric device is a device capable of measuring potential across an interface that results from a difference in the equilibrium concentrations of redox molecules in an electrochemical cell.
A xe2x80x9ccoulometric devicexe2x80x9d is a device capable of the net charge produced during the application of a potential field (xe2x80x9cvoltagexe2x80x9d) to an electrochemical cell.
An impedance spectrometer is a device capable of determining the overall impedance of an electrochemical cell.
A xe2x80x9csinusoidal voltammeterxe2x80x9d is a voltammetric device capable of determining the frequency domain properties of an electrochemical cell.
The term xe2x80x9cporphyrinic macrocyclexe2x80x9d refers to a porphyrin or porphyrin derivative. Such derivatives include porphyrins with extra rings ortho-fused, or ortho-perifused, to the porphyrin nucleus, porphyrins having a replacement of one or more carbon atoms of the porphyrin ring by an atom of another element (skeletal replacement), derivatives having a replacement of a nitrogen atom of the porphyrin ring by an atom of another element (skeletal replacement of nitrogen), derivatives having substituents other than hydrogen located at the peripheral (meso-, xcex2-) or core atoms of the porphyrin, derivatives with saturation of one or more bonds of the porphyrin (hydroporphyrins, e.g., chlorins, bacteriochlorins, isobacteriochlorins, decahydroporphyrins, corphins, pyrrocorphins, etc.), derivatives obtained by coordination of one or more metals to one or more porphyrin atoms (metalloporphyrins), derivatives having one or more atoms, including pyrrolic and pyrromethenyl units, inserted in the porphyrin ring (expanded porphyrins), derivatives having one or more groups removed from the porphyrin ring (contracted porphyrins, e.g., corrin, corrole) and combinations of the foregoing derivatives (e.g. phthalocyanines, sub-phthalocyanines, and porphyrin isomers). Preferred porphyrinic macrocycles comprise at least one 5-membered ring.
The term porphyrin refers to a cyclic structure typically composed of four pyrrole rings together with four nitrogen atoms and two replaceable hydrogens for which various metal atoms can readily be substituted. A typical porphyrin is hemin.
The term xe2x80x9cmultiporphyrin arrayxe2x80x9d refers to a discrete number of two or more covalently-linked porphyrinic macrocycles. The multiporphyrin arrays can be linear, cyclic, or branched.
A linker is a molecule used to couple two different molecules, two subunits of a molecule, or a molecule to a substrate.
A substrate is a, preferably solid, material suitable for the attachment of one or more molecules. Substrates can be formed of materials including, but not limited to glass, plastic, silicon, minerals (e.g. quartz), semiconducting materials, ceramics, metals, etc.
The term xe2x80x9codd hole oxidation statexe2x80x9d, refers to the case where the number of electron equivalents added or removed from a molecule or molecules is not an integer multiple of the number of redox-active (e.g. oxidizable or reducable) subunits in the molecule or molecules.
The phrase xe2x80x9chole hoppingxe2x80x9d refers to the exchange of oxidation states between subunits of thermodynamically similar potentials.
The term xe2x80x9carylxe2x80x9d refers to a compound whose molecules have the ring structure characteristic of benzene, naphthalene, phenanthrene, anthracene, etc. (i.e., either the 6-carbon ring of benzene or the condensed 6-carbon rings of the other aromatic derivatives). For example, and aryl group may be phenyl (C6H3) or naphthyl (C10H9). It is recognized that the aryl, while acting as substituent can itself have additional substituents (e.g. the substituents provided for Sn in the various Formulas herein).
The term xe2x80x9calkylxe2x80x9d refers to a paraffinic hydrocarbon group which may be derived from an alkane by dropping one hydrogen from the formula. Examples are methyl (CH3xe2x80x94), ethyl (C2H5xe2x80x94), propyl (CH3CH2CH2xe2x80x94), isopropyl ((CH3)2CH3xe2x80x94).
The term xe2x80x9chalogenxe2x80x9d refers to one or the electronegative elements of group VIIA of the periodic table (fluorine, chlorine, bromine, iodine, astatine).
The term xe2x80x9cnitroxe2x80x9d refers to the NO2 group.
The term xe2x80x9caminoxe2x80x9d refers to the NH2 group.
The term xe2x80x9cperfluoroalkylxe2x80x9d refers to an alkyl group where every hydrogen atom is replaced with a fluorine atom.
The term xe2x80x9cperfluoroarylxe2x80x9d refers to an aryl group where every hydrogen atom is replaced with a fluorine atom.
The term xe2x80x9cpyridylxe2x80x9d refers to an aryl group where one CH unit is replaced with a nitrogen atom.
The term xe2x80x9ccyanoxe2x80x9d refers to the xe2x80x94CN group.
The term xe2x80x9cthiocyanatoxe2x80x9d refers to the xe2x80x94SCN group.
The term xe2x80x9csulfoxylxe2x80x9d refers to a group of composition RS(O)xe2x80x94 where R is some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to methylsulfoxyl, phenylsulfoxyl, etc.
The term xe2x80x9csulfonylxe2x80x9d refers to a group of composition RSO2xe2x80x94 where R is some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not imited to methylsulfonyl, phenylsulfonyl, p-toluenesulfonyl, etc.
The term xe2x80x9ccarbamoylxe2x80x9d refers to the group of composition R1(R2)NC(O)xe2x80x94 where R1 and R2 are H or some alkyl, aryl, cycloalkyl, pertluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to N-ethylcarbamoyl, N,N-dimethylcarbamoyl, etc.
The term xe2x80x9camidoxe2x80x9d refers to the group of composition R1CON(R2)xe2x80x94 where R1 and R2 are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to acetamido, N-ethylbenzamido, etc.
The term xe2x80x9cacylxe2x80x9d refers to an organic acid group in which the OH of the carboxyl group is replaced by some other substituent (RCOxe2x80x94). Examples include, but are not limited to acetyl, benzoyl, etc
In preferred embodiments, when a metal is designated by xe2x80x9cMxe2x80x9d or xe2x80x9cMexe2x80x9d, where n is an integer, it is recognized that the metal may be associated with a counterion.
The term xe2x80x9csubstituentxe2x80x9d as used in the formulas herein, particularly designated by S or Sn where n is an integer, in a preferred embodiment refer to redox-active groups (subunits) that can be used to adjust the redox potential(s) of the subject compound. Preferred substituents include, but are not limited to, aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, amido, and carbamoyl. In preferred embodiments, a substituted aryl group is attached to a porphyrin or a porphyrinic macrocycle, and the substituents on the aryl group are selected from the group consisting of aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, amido, and carbamoyl.
Particularly preferred substituents include, but are not limited to, 4-chlorophenyl, 3-acetamidophenyl, 2,4-dichloro-4-trifluoromethyl). Preferred substituents provide a redox potential range of less than about 5 volts, preferably less than about 2 volts, more preferably less than about 1 volt.
The phrase xe2x80x9cprovide a redox potential range of less than about X voltsxe2x80x9d refers to the fact that when a substituent providing such a redox potential range is incorporated into a compound, the compound into which it is incorporated has an oxidation potential less than or equal to X volts, where X is a numeric value.